Two different ordered mesoporous carbons (OMCs) were synthesized to test their application as actinide sorbent materials: 3d-cubic FDU-16-type and 2d-hexagonal C-CS-type. A portion of each OMC was oxidized with acidic ammonium persulfate (APS), to make FDU-COOH and C-CS-COOH. All four OMCs were characterized by nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), elemental analysis, thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), and determination of the point-of-zero-charge (PZC). Based on plutonium (Pu) sorption and desorption tests with FDU-16, oxidized FDU-16-COOH, C-CS, and oxidized C-CS-COOH, the C-CS-COOH was the most effective OMC for sorption of Pu over a wide pH range. Subsequent batch experiments with Pu(VI) and Eu(III) to determine the uptake capacities, sorption kinetics, and effects of ionic strength only included C-CS and C-CS-COOH. The nature of the Pu sorption reaction was also probed via X-ray absorption spectroscopy (XAS) and TEM. The C-CS-COOH has a highly oxidized surface, open pore structure, and fairly high surface area, rendering it an effective general scavenger for actinide and lanthanide cations. Pu and Eu uptake by C-CS-COOH appears to be dictated by chemisorption, and the Langmuir Eu capacity (138 mg/g from pH 4 solution) is higher than those previously reported for several carbon materials. Pristine C-CS has a very high surface area, but a relatively low concentration of surface groups, and thus a low affinity for Eu(III). However, C-CS is an excellent sorbent of PuO2 nanocrystals, which are formed because the carbon reduces Pu(VI) and Pu(V) to Pu(IV). Plutonium is also reduced by C-CS-COOH, but PuO2 colloid formation in pH 4 solution is prevented by carboxyl complexation of Pu(IV) at the C-CS-COOH surface. Experiments are underway with Pu(IV), Np(V) and U(VI) to further explore the redox and sorption interactions of actinides with OMCs.

Sorption of plutonium and europium to ordered mesoporous carbons

248th National Meeting (2014)

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